1. Field of the Invention
The present invention relates to receiving and transmitting antennas. More particularly, the present invention relates to RF antennas having a relatively low physical volume profile. While not limited thereto, the present invention is particularly useful for high frequency RF signal exchanges at relatively low power and over short ranges.
2. Description of the Related Art
Several varieties of flat Radio Frequency (RF) antennas have evolved in the past.
U.S. Pat. No. 4,835,541 to Johnson et al provides a quarter wavelength microstrip antenna structure that includes a thin conductive copper sheet that is folded over to form the shape of the letter "U". The copper sheet, thus folded, provides an upper radiating surface section that defines a first conductive surface, a lower ground plane section that is parallel to the first section and defines a second conductive surface, and a shorting section that connects the upper and lower sections, with the upper and lower sections each meeting the shorting section at a right angle. The cavity that is defined by the upper section and the lower section is a quarter wavelength resonant cavity. A hole is drilled through the shorting section, and a coaxial cable is passed through the hole. The outer cable sheath is electrically connected to the lower section and the center cable conductor is connected to the upper section, and in one embodiment this latter connection is provided by way of an impedance matching network. The shorting section electrically connects the lower section to an edge of the upper section, thus this upper section edge is at the same potential as the lower section.
U.S. Pat. No. 5,355,142 by Marshall et al provides a quarter wave microstrip antenna having a ground plane member and a microstrip element that are generally of the same physical area, and are arranged in a mutually parallel configuration so as to define a dielectric space therebetween. The microstrip element has a length that is approximately one quarter the wavelength of the center frequency at which the antenna operates. Since the antenna is a quarter wave microstrip antenna, the microstrip element includes an L-shaped shorting element by which one edge of the microstrip element is mounted to one edge of the ground plane member by way of four metal screws that establish electrical and mechanical connection between the microstrip element and the ground plane member. A center portion of the microstrip element is cut so that a feed member may be bent downward at generally a right angle; i.e., the feed member is bent in the direction of the ground plane member. A transmission line is held by the above-described four screws and extends into the dielectric space between the microstrip element and the ground plane member. The transmission line includes a first electrical conductor that is connected to the ground plane member and a second electrical conductor that is connected to the feed member of the microstrip element.
U.S. Pat. No. 5,444,453 by Lalezari describes a parallel plate, inverted, microstrip type of antenna using air as a dielectric and intended to operate in the 10 to 40 gigaHertz range. A relatively large dielectric plate (i.e., 1.times.1 to 2.times.2 inch square or one to two inch diameter circular plates) supports a smaller metallic radiator patch centrally located over a metallic ground plane member that is about the same size as the dielectric plate. A number of support posts of substantially the same height maintain a 0.1 mm to 1.0 mm spacing between the dielectric plate and the ground plane member.
U.S. Pat. No. 5,532,707 to Klinger et al provides a directional dipole antenna wherein four dipole elements and their individual symmetrizer legs are stamped out of the material of a reflector. The four L-shaped dipole/symmetrizer units are then bent upward from the plane of the reflector by an angle of 30 to 60 or 90-degrees. In this way, the plane of the reflector meets the planes of the four L-shaped dipole/symmetrizer units to form a V-shape.